Cells start migration by generating protrusions, which require the dynamic assembly of a branched actin network and remodeling of the plasma membrane. How actin dynamics and membrane activities are coordinated during cell migration is a fundamental question in the field. The exocyst is a multiprotein complex that mediates exocytosis and polarized cell surface expansion and has recently been shown to play an important role in cell migration. We have recently found that the exocyst component Exo70 directly interacts with the Arp2/3 complex, the core machinery that nucleates actin for the generation of the branched actin network underneath the leading edges of the plasma membrane. The exocyst-Arp2/3 interaction is stimulated by epidermal growth factor (EGF), and this interaction is important for effective membrane protrusion and directional migration. We hypothesize that the exocyst plays a dual role in regulating actin dynamics through interacting with the Arp2/3 complex and physically remodeling the plasma membrane. Here we propose to investigate the molecular interactions between Exo70 and Arp2/3, and examine the effect of Exo70 on Arp2/3-mediated actin polymerization and branching. In addition, we will investigate the role of the Cdc42/Rac downstream effector kinase, Pak1, in regulating the interaction between the exocyst and Arp2/3 in response to EGF stimulation. Finally, we will examine the effect of the exocyst in the physical remodeling of the plasma membrane. Studying the molecular basis of cell migration and its regulation is important for our understanding of many physiological processes including embryogenesis and chemotaxis, and may shed light on the etiology of diseases such a neurological disorders and tumor metastasis. PUBLIC HEALTH RELEVANCE: Directional cell migration is fundamental to many physiological processes such as chemotaxis, embryogenesis, and neuronal development. Studying the molecular basis of cell migration will help us understand these physiological processes and shed light on the etiologies of diseases such as neurological disorders and cancer.